1. Field of the Invention
The present invention generally relates to computer graphics. More particularly, the present invention is directed to a system and method for creating a three-dimensional graphic object having convex or concave portions.
2. Description of the Related Art
The growing popularity of computers has enabled conventional film clips, graphics and pictures to be digitized for computer processing, allowing special visual effects never before possible. Computer imaging or graphing is also gaining a foothold in diverse professional areas such as education, science, engineering, medicine, commerce, the military, advertising, and entertainment, because of the widespread use of computers.
Referring to FIG. 1, a conventional process flow for creating a three-dimensional bounding board having a visual effect of a convex or concave character is schematically illustrated. First, a user selects a text character “A” 10 and a quadrangular shape 11 to be processed. For example, the user can select buttons directed to the required text character 10 and quadrangle 11 on pull-down or pop-up screen menus of interactive application programs to make choices. The selected text character 10 and quadrangle 11 are thereafter processed by polygon mesh modeling to generate smooth outlines and curves. As shown in FIG. 1, the text character “A” 10 is modeled by two outlines 100 and 102, where the quadrangle 11 is modeled by a closed curve 110.
Then, by using three-dimensional creating techniques, the portion 104 of the modeled text character 10 bounded by the outlines 100 and 102 is extruded to generate an extruded character 12, while the portion 112 of the modeled quadrangle 11 bounded by the closed curve 110 is extruded to generate an extruded quadrangle 13, as shown in FIG. 1. Therefore, the extruded character 12 and the extruded quadrangle 13 are composed of three-dimensional mesh data. If the user would like to create a visually convex effect on the bounding board, the extruded text character 12 is combined with the extruded quadrangle 13 to create a graphic object 14 with the convex character. If the user chooses to create a visually concave effect on the bounding board, both the extruded character 12 and the extruded quadrangle 13 are subjected to an Boolean exclusive-OR operation so as to create a graphic object 15 with the concave character.
However, prior to the formation of the convex graphic object 14 or the concave graphic object 15, the extruded quadrangle 13 should be adjusted to fit the extruded text character 12. As shown in FIG. 1, the area of the extruded quadrangle 13 should be extended so that the curve 110 can encompass the outlines 100 and 102, or, at least, the curve 110 should be tangential to the vertexes 105, 106 and 107 of character 10. However, it is quite burdensome to handle the mesh data under the three-dimensional environment.